Abstract The broad goal of this study is to elucidate basic mechanisms by which embryonic cells exert rapid spatiotemporal control over subcellular organization and force production to move, change shape, divide and execute tissue morphogenesis. Cells do this in part by patterning intracellular signals that regulate assembly and force production by the actomyosin cytoskeleton. At same time, cytoskeletal dynamics and contractility feed back to modulate the distributions and activities of their upstream regulators. A fundamental challenge is to understanding how robust spatiotemporal control of cell behavior emerges from dynamic interplay of intracellular signaling, cytoskeletal dynamics and cytomechanics, and how failures in this process produce developmental defects and human disease. We will address this challenge using the C. elegans embryo as a model system to study two fundamental, widespread and highly conserved forms of mechanochemical patterning: The first is pulsed actomyosin contractility in which the episodic assembly, contraction and disassembly of contractile networks drive transient deformations of the cell surface to control cell shape change, cortical flow and tissue deformation. The second is dynamic formation and stabilization of cortical polarity through interactions among conserved PAR polarity proteins, Rho family GTPases and the actomyosin cytoskeleton. C. elegans embryos provide a unique opportunity to study these processes at the surface of single large cells in vivo using quantitative microscopy and well-developed tools for genetic manipulation. Building on our previous studies, we will use a tightly integrated combination of quantitative imaging, experimental manipulations, and predictive computer simulations to address the following questions: 1) How do tunable spatiotemporal dynamics of pulsed contractility emerge from dynamic coupling of RhoA signaling and actomyosin contractility? 2) How are stable boundaries between polarized domains maintained in the face of continuous exchange and diffusion, through dynamic clustering, positive feedback and mutual antagonism of polarity proteins? 3) How is the polarity boundary maintained in the face of persistent contractile asymmetries through feedback mechanisms that couple PAR proteins, small GTPases and actomyosin contractility? Because the molecular players involved in these processes are highly conserved, our work will have direct relevance for understanding cell polarity and spatiotemporal control of actomyosin contractility in many other contexts, both in health and disease.